High-sensitivity controllable mechanical discoloration colloidal crystal hydrogel material and preparation method thereof

Abstract

The invention discloses a high-sensitivity controllable mechanical discoloration colloidal crystal hydrogel material and a preparation method thereof, and particularly relates to the field of colloidal crystal materials, the high-sensitivity controllable mechanical discoloration colloidal crystal hydrogel material comprises an elastic hydrogel base layer and a layer number controllable colloidal crystal film; the hydrogel base layer has stretchable and compressible properties, and the colloidal crystal film is formed by periodically arranging monodisperse colloidal particles and can generate Bragg diffraction with electromagnetic waves so as to generate structural colors. When the hydrogel base layer is subjected to stretching or compression stimulation, the volume of the hydrogel base layer is deformed, so that the distance between the colloidal crystals is changed, a reflection peak is displaced, and high-sensitivity detection of strain is realized. The prepared mechanical color-changing sensor has the characteristics of high sensitivity and high stability, and can be used in the fields of strain sensors, health monitoring, anti-counterfeiting materials and the like.

Description

Technical Field

[0001] The present invention belongs to the technical field of colloidal crystal materials, and particularly relates to a highly sensitive and controllable mechanically color-changing colloidal crystal hydrogel material and a preparation method thereof. Background Art

[0002] In recent years, the demand for flexible wearable devices in the fields of human health monitoring, human motion monitoring, and human-computer interaction has been increasing. However, most traditional strain sensors are based on materials such as rigid semiconductors, metals, and ceramics, which have problems such as poor ductility and brittleness, and it is difficult to meet the requirements of flexible wearable devices. Mechanically color-changing photonic crystals provide a new idea for strain sensors due to their unique color-changing principle, that is, by changing the crystal plane spacing under external force, and then changing their structural color.

[0003] Most of the existing technologies adopt the method of embedding colloidal microspheres into an elastic substrate to achieve the effect of mechanical color change by changing the crystal spacing. However, there is a lack of effective interfacial bonding force between the hard microspheres and the elastic substrate, resulting in phase separation. Therefore, the presence of microspheres will affect the mechanical properties of the elastic substrate and limit the mechanical sensing performance. Moreover, the reported mechanically color-changing photonic crystals have problems such as low sensitivity, slow response speed, and small wavelength adjustable range due to the small crystal plane spacing, which limits their application range. Chinese Patent with Publication No. CN117664008B discloses a stretchable photonic crystal strain sensor with a red-shift mechanical color change response. The colloidal crystal film is embedded in an elastic substrate, and strain detection is achieved through the form of wavelength red-shift. This method has the advantages of being fast, simple, non-toxic and harmless to materials, and high stability. However, this method requires embedding the colloidal crystal into the elastic matrix, resulting in a smaller refractive index difference between the colloidal particles and the surrounding medium, affecting the color vividness, and thus amplifying the sensing error. Summary of the Invention

[0004] In order to solve the deficiencies of the existing technology, the purpose of the present invention is to provide a highly sensitive and controllable mechanically color-changing colloidal crystal hydrogel material and a preparation method thereof, to solve the problem that the existing photonic crystal hydrogel strain sensor cannot simultaneously be compatible with high sensitivity and high elasticity, thereby improving the sensitivity, response speed and elongation rate of the sensor, and expanding the functionality and practicality of the colloidal crystal hydrogel strain sensing material.

[0005] To solve the above technical problems, an embodiment of the present invention provides a highly sensitive and controllable mechanically color-changing colloidal crystal hydrogel material, including a hydrogel base layer for providing support, stretchability and compressibility properties, and a colloidal crystal thin film attached to the hydrogel base layer for generating structural color and driving the hydrogel base layer to deform by applying an external force;

[0006] The number of layers of the colloidal crystal thin film is controllable and is obtained by self-assembly at the gas-liquid interface and then transferred to the surface of the hydrogel base layer.

[0007] Preferably, the number of layers of the colloidal crystal film is 1 - 20 layers.

[0008] Among them, the colloidal crystal film is formed by the ordered arrangement of monodisperse colloidal particles, and the particle size of the monodisperse colloidal particles is 100 - 300 nm.

[0009] Among them, the monodisperse colloidal particles include SiO2 colloidal microspheres, polystyrene colloidal microspheres, poly(methyl methacrylate) microspheres, and hybrid polymer microspheres;

[0010] The hybrid polymer microspheres are copolymerized from two or more monomers among styrene, methyl methacrylate, butyl acrylate, and acrylic acid.

[0011] Preferably, the thickness of the hydrogel base layer is 0.5 - 5 mm.

[0012] Among them, the hydrogel base layer is obtained by ultraviolet light-induced polymerization of a prepolymer solution of a high molecular monomer; the high molecular monomer is one or several of acrylic acid, acrylamide, 2-hydroxyethyl acrylate, benzyl acrylate, isobutyl methacrylate, and 2-methoxyethyl acrylate.

[0013] Among them, in the prepolymer solution of the high molecular monomer, the mass percentage of 2-hydroxyethyl acrylate is 40 - 100%.

[0014] The present invention also provides a preparation method of a highly sensitive and controllable mechanically chromogenic colloidal crystal hydrogel material, including the following steps:

[0015] S1. Preparation of the hydrogel base layer: Mix a high molecular monomer, other comonomers, a crosslinking agent, and a photoinitiator uniformly in a solvent, then inject the mixture into a cavity with one end open, and carry out a polymerization reaction under ultraviolet light irradiation;

[0016] S2. Preparation of a single-layer colloidal crystal film: Mix a colloidal microsphere emulsion with ethanol to obtain a colloidal microsphere mixture, continuously inject the colloidal microsphere mixture from the air / water interface at a constant flow rate, and after the microspheres diffuse to the water-air interface, let it stand for 30 - 40 min;

[0017] S3. Preparation of a single-layer colloidal crystal hydrogel composite film: Attach the hydrogel film to the surface of a glass slide, obliquely insert it into the air / water interface at a 45-degree angle, and gently lift it up to transfer the single-layer colloidal crystal film to the surface of the hydrogel film;

[0018] S4. Preparation of a multi-layer colloidal crystal hydrogel composite film: Repeat steps S2 and S3 to obtain a multi-layer colloidal crystal hydrogel composite film, and prepare a highly sensitive and controllable mechanically chromogenic colloidal crystal hydrogel material.

[0019] Among them, in step S1, the polymer monomer is hydroxyethyl acrylate;

[0020] The crosslinking agent is one or a mixture of several of N,N'-methylenebisacrylamide, divinylbenzene, and polyethylene glycol diacrylate;

[0021] The mass of the crosslinking agent is 0.1-0.4% of the mass of the polymer monomer.

[0022] Among them, in step S1, the photoinitiator is one of 2-hydroxy-2-methylpropiophenone and diphenyl-(2,4,6-trimethylbenzoyl)phosphine oxide;

[0023] The mass of the photoinitiator is 0.05-0.1% of the mass of the polymer monomer.

[0024] Among them, in step S1, the solvent is one of water, ethanol, and ethylene glycol;

[0025] The dosage of the solvent is 10-50% of the mass of the polymer monomer.

[0026] Among them, in step S1, the time of the UV curing reaction is 5-30 min, and the UV light wavelength is 365 nm.

[0027] Among them, in step S2, in the colloidal microsphere emulsion and ethanol mixture, the mass ratio of colloidal microspheres, ethanol, and water is: (0.1-0.4):(0.5-1.5):1.

[0028] Among them, in step S2, the flow rate of injecting the colloidal microsphere mixture into the air / water interface is 0.1-4 mL / h.

[0029] The beneficial effects of the above technical solutions of the present invention are as follows:

[0030] 1. The highly sensitive and controllable mechanically chromogenic colloidal crystal hydrogel strain sensing material proposed by the present invention is composed of a hydrogel substrate and a colloidal crystal thin film. The hydrogel substrate plays a supporting role, and the structural color is generated by Bragg diffraction on the surface colloidal crystal thin film. Due to the abundant free chemical bonds on the surface of the hydrogel substrate, there is a strong binding force at the interface between the two phases, which can make the colloidal particles stably adhere to the surface of the hydrogel substrate. Therefore, when subjected to an external force, the structure of the highly sensitive and controllable mechanically chromogenic colloidal crystal hydrogel material can be maintained stable.

[0031] 2. The present invention obtains a two-dimensional colloidal crystal structure by the layer-by-layer assembly method, and this two-dimensional colloidal crystal structure has the characteristic of controllable number of layers. By changing the particle size of each layer of colloidal particles, homogeneous and heterogeneous structure colloidal crystals can be prepared, and thus colloidal crystal films with double bandgap or multi-bandgap positions can be obtained. When deformed, the colloidal crystal thin films at different bandgap positions can all produce reflection peak shifts, thereby improving the detection accuracy.

[0032] 3. In the present invention, the colloidal crystal thin films are arranged layer by layer in a single layer or several layers, with a thickness between 200 - 1000 nm. Even a slight deformation can cause an obvious displacement of the reflection peak, which can effectively improve the detection sensitivity. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 It is a graph showing the relationship between the force value, the position of the reflection peak, and the displacement in Embodiment 1 of the present invention;

[0034] Figure 2 It is a graph showing the relationship between the force value, the position of the reflection peak, and the displacement in Embodiment 2 of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0035] To make the technical problems, technical solutions, and advantages to be solved by the present invention clearer, the following will be described in detail with reference to the accompanying drawings and specific embodiments.

[0036] Embodiment 1

[0037] S1.1. Preparation of the hydrogel base layer: Hydroxyethyl acrylate, acrylic acid, N,N'-methylenebisacrylamide, and 2-hydroxy-2-methylpropiophenone were added to water in a mass ratio of 50:50:0.15:0.06. The amount of solvent water used was 15% of the mass of the polymer monomers. After complete dissolution, the bubbles were removed, and it was injected into a transparent cavity with one end open and a thickness of 0.8 mm, and cured under ultraviolet light for 10 min to obtain a unsupported hydrogel film with a thickness of 0.6 mm.

[0038] S1.2. Preparation of the single-layer colloidal crystal film: Monodisperse SiO2 colloidal microspheres with a particle size of 185 nm were dispersed in a mixed solution of water and ethanol. The mass ratio of the colloidal microspheres, ethanol, and water was: 0.15:0.5:1. After uniform dispersion, it was continuously injected into the water surface from the air / water interface at a flow rate of 0.1 mL / h. After the microspheres diffused to the water-vapor interface, it was left standing for 30 min.

[0039] S1.3. Preparation of the single-layer colloidal crystal hydrogel composite film: The hydrogel film was attached to the surface of a glass slide and obliquely inserted into the air / water interface at a 45-degree angle, and gently lifted upward, then the single-layer colloidal crystal film could be transferred to the surface of the hydrogel film. Repeating this step can obtain colloidal crystal films with different numbers of layers.

[0040] Embodiment 2

[0041] S2.1. Preparation of the hydrogel substrate: Add hydroxyethyl acrylate, acrylic acid, benzyl acrylate, divinylbenzene, and diphenyl-(2,4,6-trimethylbenzoyl)phosphine oxide into ethylene glycol according to the mass ratio of 45:30:25:0.25:0.08. The amount of ethylene glycol used is 30% of the mass of the polymer monomers. After complete dissolution, remove the bubbles, inject it into a transparent cavity with one end open and a thickness of 1 mm, and cure it under ultraviolet light for 20 min to obtain a unsupported hydrogel film with a thickness of 0.85 mm.

[0042] S2.2. Preparation of the single-layer colloidal crystal film: Disperse monodisperse polystyrene colloidal microspheres with a particle size of 220 nm in a mixed solution of water and ethanol. The mass ratio of the colloidal microspheres, ethanol, and water is 0.25:1:1. After uniform dispersion, continuously inject it into the water surface from the air / water interface at a flow rate of 0.5 mL / h. After the microspheres diffuse to the water-vapor interface, let it stand for 30 min.

[0043] S2.3. Preparation of the single-layer colloidal crystal hydrogel composite film: Attach the hydrogel film to the surface of a glass slide, insert it obliquely into the air / water interface at a 45-degree angle, and gently lift it up to transfer the single-layer colloidal crystal film to the surface of the hydrogel film. Repeat this step to obtain colloidal crystal films with different numbers of layers.

[0044] Example 3

[0045] S3.1. Preparation of the hydrogel substrate: Add hydroxyethyl acrylate, isobutyl methacrylate, 2-methoxyethyl acrylate, polyethylene glycol diacrylate, and 2-hydroxy-2-methylpropiophenone into ethylene glycol according to the mass ratio of 55:20:25:0.38:0.08. The amount of ethylene glycol used is 30% of the mass of the polymer monomers. After complete dissolution, remove the bubbles, inject it into a transparent cavity with one end open and a thickness of 3 mm, and cure it under ultraviolet light for 20 min to obtain a unsupported hydrogel film with a thickness of 2.5 mm.

[0046] S3.2. Preparation of the single-layer colloidal crystal film: Disperse monodisperse hybrid styrene microspheres with a particle size of 165 nm in a mixed solution of water and ethanol. The mass ratio of the colloidal microspheres, ethanol, and water is 0.25:1:1. After uniform dispersion, continuously inject it into the water surface from the air / water interface at a flow rate of 3 mL / h. After the microspheres diffuse to the water-vapor interface, let it stand for 30 min.

[0047] S3.3. Preparation of the single-layer colloidal crystal hydrogel composite film: Attach the hydrogel film to the surface of a glass slide, insert it obliquely into the air / water interface at a 45-degree angle, and gently lift it up to transfer the single-layer colloidal crystal film to the surface of the hydrogel film.

[0048] S3.4 Preparation of colloidal crystal film with multiple bandgap positions: Monodisperse hybrid styrene microspheres with a particle size of 220 nm are dispersed in a mixed solution of water and ethanol. The mass ratio of colloidal microspheres, ethanol, and water is 0.25:1:1. After uniform dispersion, it is continuously injected into the water surface from the air / water interface at a flow rate of 3 mL / h. After the microspheres diffuse to the water-vapor interface, it is left standing for 30 min. A hydrogel film with a monolayer of 165-nm colloidal crystals is attached to the surface of a glass slide and obliquely inserted into the air / water interface at a 45-degree angle, and gently lifted upward. The monolayer colloidal crystal film is transferred to the surface of the hydrogel film. Thus, a hydrogel colloidal crystal film with a heterostructure can be obtained.

[0049] Mechanical response test:

[0050] The colloidal crystal sensor prepared in Example 1 is cut into a rectangle with a length of 4 cm and a width of 2 cm, and the change in the reflection peak under a certain stress stimulation in the length direction is tested. The test results are as Figure 1 shown. When the stress range is 0 cN - 40 cN, the hydrogel undergoes a displacement of 0 - 0.23 mm, the reflection peak position redshifts from 430 nm to 550 nm, and the structural color changes from purple to green.

[0051] The colloidal crystal sensor prepared in Example 2 is cut into a rectangle with a length of 4 cm and a width of 2 cm, and the change in the reflection peak under a certain stress stimulation in the length direction is tested. The test results are as Figure 2 shown. When the stress range is 0 cN - 66 cN, the hydrogel undergoes a displacement of 0 - 0.31 mm, the reflection peak position redshifts from 520 nm to 650 nm, and the structural color changes from green to red.

[0052] The colloidal crystal sensor prepared in Example 3 has two reflection peaks, located at 430 nm and 520 nm respectively. It is cut into a rectangle with a length of 4 cm and a width of 2 cm, and the change in the reflection peak under a certain stress stimulation in the length direction is tested. When the stress range is 0 cN - 72 cN, the hydrogel undergoes a displacement of 0 - 0.36 mm, and the reflection peak positions redshift from 430 nm to 590 nm and from 520 nm to 630 nm respectively.

[0053] The beneficial effects of the above technical solutions of the present invention are as follows:

[0054] 1. The highly sensitive and controllable mechanically chromogenic colloidal crystal hydrogel strain sensing material proposed by the present invention is composed of a hydrogel substrate and a colloidal crystal thin film. The hydrogel substrate plays a supporting role, and the structural color is generated by the colloidal crystal thin film on the surface due to Bragg diffraction. Due to the abundant free chemical bonds on the surface of the hydrogel substrate, there is a strong binding force at the interface between the two phases, which can stably attach the colloidal particles to the surface of the hydrogel substrate. Therefore, when subjected to external forces, the structure of the highly sensitive and controllable mechanically chromogenic colloidal crystal hydrogel material can be maintained stable.

[0055] 2. The present invention obtains a two-dimensional colloidal crystal structure through the layer-by-layer assembly method, and this two-dimensional colloidal crystal structure has the characteristic of controllable number of layers. By changing the particle size of colloidal particles in each layer, homogeneous and heterogeneous structured colloidal crystals can be prepared, and thus colloidal crystal films with double-bandgap or multi-bandgap positions can be obtained. When subjected to deformation, the colloidal crystal thin films at different bandgap positions can all produce reflection peak shifts, thereby improving the detection accuracy.

[0056] 3. In the present invention, the colloidal crystal thin films are arranged layer by layer in a single layer or several layers, with a thickness between 200 - 1000 nm. Even a slight deformation can produce an obvious reflection peak shift, which can effectively improve the detection sensitivity.

[0057] The above is the preferred embodiment of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle described in the present invention, several improvements and refinements can still be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A highly sensitive and controllable mechanically chromogenic colloidal crystal hydrogel material, characterized in that, It includes a hydrogel substrate for providing support, stretchability and compressibility properties, and a colloidal crystal film attached to the hydrogel substrate for generating structural color and driving the deformation of the hydrogel substrate by applying an external force. The number of layers of the colloidal crystal film is controllable and is obtained by self-assembly at the gas-liquid interface and then transferred to the surface of the hydrogel substrate.

2. The highly sensitive and controllable mechanically color-changing colloidal crystal hydrogel material according to claim 1, wherein The number of layers of the colloidal crystal film is 1-20 layers, and the thickness of the hydrogel substrate is 0.5-5 mm.

3. The highly sensitive and controllable mechanically color-changing colloidal crystal hydrogel material according to claim 1, wherein The colloidal crystal film is formed by the ordered arrangement of monodisperse colloidal particles, and the particle size of the particles is 100-300 nm. The monodisperse colloidal particles include SiO2 colloidal microspheres, polystyrene colloidal microspheres, poly(methyl methacrylate) microspheres, and hybrid polymer microspheres. The hybrid polymer microspheres are copolymerized from two or more monomers among styrene, methyl methacrylate, butyl acrylate, and acrylic acid.

4. The highly sensitive and controllable mechanically color-changing colloidal crystal hydrogel material according to claim 1, wherein The hydrogel substrate is obtained by ultraviolet light-initiated polymerization of a high molecular monomer pre-gel solution; the high molecular monomer is one or several of acrylic acid, acrylamide, 2-hydroxyethyl acrylate, benzyl acrylate, isobutyl methacrylate, and 2-methoxyethyl acrylate, and the mass percentage of 2-hydroxyethyl acrylate is 40-100%.

5. A preparation method of a highly sensitive and controllable mechanically color-changing colloidal crystal hydrogel material as described in any one of claims 1-4, characterized in that, It includes the following steps: S1. Preparation of the hydrogel substrate: Mix the high molecular monomer, comonomer, crosslinker, and photoinitiator evenly in a solvent, then inject it into a cavity with one end open, and carry out a polymerization reaction under ultraviolet light irradiation. S2. Preparation of a single-layer colloidal crystal film: Mix the colloidal microsphere emulsion with ethanol to obtain a colloidal microsphere mixture, continuously inject the colloidal microsphere mixture from the air / water interface at a constant flow rate, and after the microspheres diffuse to the water-gas interface, let it stand for 30-40 min. S3. Preparation of a single-layer colloidal crystal hydrogel composite film: Attach the hydrogel film to the surface of a glass slide, insert it obliquely into the air / water interface at a 45-degree angle, and lift it forward to transfer the single-layer colloidal crystal film to the surface of the hydrogel film. S4. Preparation of a multi-layer colloidal crystal hydrogel composite film: Repeat steps S2 and S3 to obtain a multi-layer colloidal crystal hydrogel composite film, and prepare a highly sensitive and controllable mechanically color-changing colloidal crystal hydrogel material.

6. The preparation method of the highly sensitive and controllable mechanically color-changing colloidal crystal hydrogel material according to claim 8, characterized in that, In step S1, the high molecular monomer is 2-hydroxyethyl acrylate. The crosslinker is one or several mixtures of N,N'-methylenebisacrylamide, divinylbenzene, and polyethylene glycol diacrylate. The mass of the crosslinker is 0.1-0.4% of the mass of the high molecular monomer.

7. The preparation method of the highly sensitive and controllable mechanically color-changing colloidal crystal hydrogel material according to claim 8, characterized in that, In step S1, the photoinitiator is one of 2-hydroxy-2-methylpropiophenone and diphenyl-(2,4,6-trimethylbenzoyl)phosphine oxide. The mass of the photoinitiator is 0.05-0.1% of the mass of the high molecular monomer.

8. The preparation method of the highly sensitive and controllable mechanically color-changing colloidal crystal hydrogel material according to claim 8, characterized in that, In step S1, the solvent is one of water, ethanol, and ethylene glycol. The dosage of the solvent is 10-50% of the mass of the high molecular monomer.

9. The preparation method of the highly sensitive and controllable mechanically color-changing colloidal crystal hydrogel material according to claim 8, characterized in that, In step S1, the time of the ultraviolet curing reaction is 5-30 min, and the wavelength of the ultraviolet light is 365 nm.

10. The preparation method of the highly sensitive and controllable mechanically color-changing colloidal crystal hydrogel material according to claim 8, characterized in that, In step S2, in the mixture of the colloidal microsphere emulsion and ethanol, the mass ratio of the colloidal microspheres, ethanol, and water is: (0.1-0.4):(0.5-1.5):

1. In step S2, the flow rate of the colloidal microsphere mixture injected into the air / water interface is 0.1 - 4 mL / h.

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